Rotary furnaces of the plasma-arc heating type

ABSTRACT

The furnace is provided at each end with a chamber placed opposite to the moving enclosure of the furnace and limited by a casing attached to the stationary enclosure. The chamber is made leak-tight with respect to the moving enclosure by means of at least one torus supplied with gas at a pressure which is higher than the pressure within the chamber. A continuous curtain of gas is thus formed between the torus and a front plate which is attached to the moving enclosure.

United States Patent 1191 Schoumaker et al. I

1451 Aug. 20, 1974 ROTARY FURNACES OF THE PLASMA-ARC HEATING TYPE Inventors: Henry Schoumaker, Bruxelles;

David Yerouchalmi, Le-Mesnil-Saint-Denis, both of France Assignee: Commissariat a lEnergie Atomique,

Paris, France Filed: Sept. 27, 1973 Appl. No.: 401,230

Foreign Application Priority Data Oct. 6, 1972 France 72.35622 US. Cl 13/9, 219/121 P Int. Cl. H05b 7/18 Field of Search l3/l,9, 3l;2l9/12lP [56] References Cited UNITED STATES PATENTS 3,286,012 11/1966 FOeX..... 219/121 P 3,697,660 10 1972 Frolov 219 121 P Primary Examiner-R. N. Envall 7 ABSTRACT The furnace is provided at each end with a chamber placed opposite to the moving enclosure of the furnace and limited by a casing attached to the stationary enclosure. The chamber is made leak-tight with respect to the moving enclosure by means of at least one torus supplied with gas at a pressure which is higher than the pressure within the chamber. A continuous curtain of gas is thus formed between the torus and a front plate which is attached to the moving enclosure.

7 Claims, 5 Drawing Figures r 7 4 8 a i i ROTARY FURNACES OF THE PLASMA-ARC HEATING TYPE This invention relates to improvements in rotary furnaces which operate on the plasma-arc heating principle.

More specifically, the present invention is concerned with the construction of a leak-tight lock-chamber placed at least at one end of the rotary furnace in order to permit the introduction of a controlled atmosphere into said furnace. Said device is particularly well suited to the plasma-arc furnace claimed in French Patent No. 1,526,999 in the name of Commissariat a IEnergie Atomique.

For the production of special alloys or for the treatment of refractory products, it is necessary to ensure that the internal atmosphere of the furnace is strictly proportioned and controlled (oxidizing, reducing, neutral). The ambient air must therefore be prevented from penetrating into said enclosure and from modifying the atmosphere of the furnace.

In order to obtain this result, one solution would consist in placing the entire furnace within a leak-tight enclosure but this would not produce the desired result. Provision must in fact be made for vaporization of water on the external walls of the furnace in order to cool this latter and said water vapor would have the effect of contaminating the gas mixture within the furnace.

In order to overcome this disadvantage, there can be formed at each end of the rotating portion of the furnace a leak-tight chamber or lock-chamber in which the desired gas mixture can be injected and which communicates with the interior of the furnace.

The difficulty lies in the fact that the furnace rotates about an axis whereas the lock-chamber must be stationary in order to permit the admission of the gas mixture.

Leak-tightness between the stationary portion and the rotating portion must achieve a particularly high standard since it has to be maintained between two different gases, namely on the one hand the gas mixture and on the other hand the cooling water vapor. Since the temperature conditions are very severe, it is very difficult to use a frictional bearing disc.

This invention is particularly directed to an improvement in rotary plasma-arc furnaces and is distinguished by the fact that the furnace is provided at each end with a chamber placed opposite to the moving enclosure of said furnace. Each chamber abuts a casing attached to the stationary enclosure is made leak-tight with respect to the moving enclosure by means rigidly fixed to the stationary enclosure so as to form a continuous gas curtain between said means and a front plate attached to the moving enclosure, a clearance being provided between said means and said plate.

In a preferred embodiment, the means for forming the gas curtain includes at least one torus havingthe same axis as the furnace, each torus being rigidly fixed to one end of a shell whilst the other end of said shell is rigidly fixed to the stationary enclosure. Each toms is partially housed within a portion of the front plate which has a concave surface of revolution, at least one of the tori being provided, on that surface which faces said plate, with calibrated orifices. Each torus is further provided with pipes for the admission of gas into each torus at a pressure which is higher than the pressure existing within said chamber.

In other words, a gas jet under pressure is produced between the moving portion and the stationary portion of the furnace. The gas employed is either identical with the gas to be injected into the fumace or compatible with the latter. This accordingly avoids the need for any friction seal which would in any case not ensure a sufficient degree of leak-tightness against the gases employed and which would further result in an increase in the energy required for setting the furnace in rotation.

A better understanding of the invention will in any case be obtained from the following description of one embodiment of the invention which is given by way of non-limitative example, reference being had to the accompanying figures, in which:

FIG. 1 is a partial external view, partially in crosssection showing part of the furnace in accordance with the invention;

FIG. 2 shows a number of alternative forms of construction of the dynamic seal.

FIG. 1 shows the main constructional features of the rotary furnace of the plasma-arc heating type as described in French Patent No. l,526,999 cited in the foregoing. In particular, said furnace comprises a stationary enclosure 1 and a moving enclosure 2 rotatably mounted within said enclosure 1 on bearings such as 3 which are carried by the latter. The moving enclosure 2 has a substantially cylindrical central portion, the ends of which terminate in conical portions. Only one conical portion 15 is shown in the drawing in order to avoid complication of the illustration whilst the other end is identical with the first except for a few secondary details. Provision is made on the external surface of the moving enclosure 2 for a crown-wheel 4 provided with a set of teeth 5 disposed in meshing engagement with a bevel pinion 6 which is fixed on the end of a driving shaft 7. Said shaft is driven in rotation about its own axis by driving means (not shown in the drawings) and rotatably mounted on support bearings 8 and 9 which are mounted within a guide sleeve 10, said sleeve being rigidly fixed on a frame 11 which is attached to the stationary enclosure 1. External cooling of the stationary enclosure 1 and of the moving enclosure 2 is carried out by means of a manifold 12 which is supplied in particular with water under pressure through connectingpipes 13. Said manifold 12 is intended to deliver the water contained therein into spray tubes 14 so as to cause said water to circulate between the conical end portion 15 of the moving enclosure 2 and a front plate 16 which is substantially perpendicular to the axis of rotation of said enclosure. Said front plate 16 is rigidly fixed to the corresponding end of said moving enclosure.

The stationary enclosure 1 has a sheet-metal extension 18 of generally cylindrical shape and rigidly fixed to said enclosure 1. The chamber is closed by a plate 19 which is attached to the sheet-metal extension 18.

In order to form the leak-tight lock-chamber 20 which communicates with the furnace 2 through the opening 21, a cylindrical shell 22 is rigidly fixed to the plate 19. Said shell 22 terminates at the end which is not attached to the plate 19 in a hollow torus 23 which thus completely surrounds the nose 21 of the furnace 2. The plate 16 is provided along its periphery with a surface 24 having a conical shape and the torus 23 is engaged in the opening of said concave surface without coming into contact with the latter. The torus 23 is provided with calibrated orifices such as 25 which are uniformly spaced over that portion of surface of said torus which faces the concave surface 24. The hollow torus 23 is further provided with a gas admission pipe 26 which passes through the plate 19.

Accordingly, the leak-tight chamber 20 is defined n the one hand by the plate 16 rotates with the furnace 2, and on the other hand by the shell 22 and the torus 23 which are stationary since they are rigidly fixed to the plate 19. The plate 1 is traversed by a pipe 27 for the admission of the gas or gas mixture which is intended to form the atmosphere of the furnace and by the plasma gun 28, this latter being fitted with a static seal 29 which is secured to the plate 19.

Cooling pipes 30 are also placed on the external face of the plate 19.

Although the torus 23 has been given a circular cross-section in FIG. 1, it must nevertheless be understood that a circular shape is in no way necessary. FIG. 2 shows a number of alternative designs of said torus 23.

In FIG. 2a, the torus has a circular cross-section as in FIG. 1.

In FIG. 2b, the torus 23 also has a circular crosssection but is provided on that face which is located opposite to the surface 24 with splines 31 formed between the orifices 25 of the torus 23. Said splines thus form the equivalent of baffles and the seal thus provided is even further enhanced.

FIG. 2c shows a torus having an oval cross-section.

In FIG. 2d, the sealing system comprises on the one hand a torus 23 which is identical with the torus described in the foregoing and on the other hand, a second torus 23' which is provided in addition with a deformable wall 32 without any orifice. Said second torus is fitted with a pipe 26 for the admission of gas under pressure. Said second torus 23' cooperates with a second concave surface 24 which is formed in the front plate 16.

The operation of the sealing device which is shown in FIG. 2d is as follows: when the furnace is being rotated, only the torus 23' is supplied with gas, with the result that a gas curtain is thus formed and ensures leak-tightness. When the torus 23' is put under pressure, its wall 32 is deformed and comes into intimate contact with the portion 24 of the front plate 16, thus forming a seal between the lock-chamber and the remainder of the enclosure. When the furnace is not in motion, this mode of operation serves to provide a static seal which is favorable both to the production of a vacuum and to the removal of gases contained in the charge. When the cylindrical furnace is in motion, the torus 23' serves to regulate the leakage flow rate of the gas which is discharged from the torus 23. The gas which is injected into the tori 23 can be either identical with the gas which is introduced through the pipe 27 into the lock-chamber 20 and which will therefore constitute the atmosphere of the furnace or may altematively be different but must nevertheless remain compatible with the first gas. The pressure of the gas injected into the torus 23 is slightly higher than that which prevails within the enclosure 1 and within the lock-chamber 20. There is thus no leakage of gas from the enclosure 1 to the lock-chamber 20.

It is wholly apparent that the sealing device could also be very readily constituted by two coaxial tori which are identical with the torus 23 and cooperate with two portions of concavesurface 24.

What we claim is:

1. A plasma-arc furnace comprising:

a rotatable cylindrical furnace body having an opening in at least one end thereof adapted to admit a plasma arc;

a stationary enclosure adjacent to said opening;

a plasma heat source mounted in said stationary enclosure for generating the plasma arc;

an annular plate member secured to said end of said cylindrical portion and surrounding said opening; and

sealing means mounted within said stationary enclosure for ejecting a gas directly against said plate member to form a fluid seal therewith.

2. A plasma-arc furnace comprising:

a rotatable cylindrical furnace body having an opening in at least one end thereof adapted to admit a plasma arc;

a stationary enclosure adjacent to said opening;

a plasma heat source mounted in said stationary enclosure for generating the plasma arc;

an annular plate member secured to said end of said cylindrical portion and surrounding said opening, said plate member having a circumferential groove in a surface facing said stationary enclosure;

sealing means comprising a toroidal ring member mounted within said stationary enclosure and having a portion thereof situated within said groove in said plate member in a spaced relationship therewith;

means for supplying a gas to said ring member; and

at least one orifice in said ring member for ejecting said gas against said plate member to form a fluid seal therewith.

3. The furnace of claim 2 wherein said ring member has a circular cross-section.

4. The furnace of claim 2 wherein said ring member has an oval cross-section.

5. The furnace of claim 2 wherein said ring member has a plurality of splines extending from an outer surface of said portion of said ring member which is in said groove.

6. The furnace of claim 2 further comprising second sealing means mounted within said stationary enclosure for providing a static seal with said plate member.

7. The furnace of claim 2 wherein said plate member is further provided with a second circumferential groove; and wherein said second sealing means comprises:

a second toroidal ring member having a portion thereof situated within said second groove in a spaced relationship therewith, said ring member having a deformable surface adjacent to said second groove, and means for urging said deformable surface into contact with said plate member.

V UNITED STATES PATENT OFFICE CERTIFICATE OF 'CORRECTION Patent No. 3,3 ,95 Dated August 20. 1974 lnve fl Henry Schoumaker et al It is certifiedthat error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown below:

In column 2, line 18, delete "partial external" and insert --fragmentary elevational--; In column 3, line 10 after "16" insert -.--wh'ich-;

In column 4, line 54; (claim 7), delete "2" and insert 6-.

Signed'end sealedthislOth dayof December 1974.

(SEAL) ,Attest: v v

McCOY M. GIBSON JR. C. MARSHALL DANN Y Attesting Officer Commissioner of Patents FORM po'wso Q Q t I Q uscoMM-ocoosn-eu 1* U.S.' GD VERI IMENT PRINTING OFFICE lili O-dil-Sll. 

1. A plasma-arc furnace comprising: a rotatable cylindrical furnace body having an opening in at least one end thereof adapted to admit a plasma arc; a stationary enclosure adjacent to said opening; a plasma heat source mounted in said stationary enclosure for generating the plasma arc; an annular plate member secured to said end of said cylindrical portion and surrounding said opening; and sealing means mounted within said stationary enclosure for ejecting a gas directly against said plate member to form a fluid seal therewith.
 2. A plasma-arc furnace comprising: a rotatable cylindrical furnace body having an opening in at least one end thereof adapted to admit a plasma arc; a staTionary enclosure adjacent to said opening; a plasma heat source mounted in said stationary enclosure for generating the plasma arc; an annular plate member secured to said end of said cylindrical portion and surrounding said opening, said plate member having a circumferential groove in a surface facing said stationary enclosure; sealing means comprising a toroidal ring member mounted within said stationary enclosure and having a portion thereof situated within said groove in said plate member in a spaced relationship therewith; means for supplying a gas to said ring member; and at least one orifice in said ring member for ejecting said gas against said plate member to form a fluid seal therewith.
 3. The furnace of claim 2 wherein said ring member has a circular cross-section.
 4. The furnace of claim 2 wherein said ring member has an oval cross-section.
 5. The furnace of claim 2 wherein said ring member has a plurality of splines extending from an outer surface of said portion of said ring member which is in said groove.
 6. The furnace of claim 2 further comprising second sealing means mounted within said stationary enclosure for providing a static seal with said plate member.
 7. The furnace of claim 2 wherein said plate member is further provided with a second circumferential groove; and wherein said second sealing means comprises: a second toroidal ring member having a portion thereof situated within said second groove in a spaced relationship therewith, said ring member having a deformable surface adjacent to said second groove, and means for urging said deformable surface into contact with said plate member. 